The proposed study has the primary objective of investigating the transport and deposition of hygroscopic aerosols in the human respiratory tract, using physical models of the larynx and tracheobronchial tree. Emphasis will be placed on deposition in the airways with partial obstruction, which arises in patients with various types of lung diseases. The proposed study is both expezimental and theoretical in nature. In the experimental part, physical models of the larynx and tracheobronchial tree will be used to investigate the effects of particle size, chemical composition of the particles, and air flow on deposition rates. In the theoretical analysis, the problems of flow and deposition in well-defined passageways corresponding to the partially obstructed airways will be investigated. The long-term objective of the project is to develop a mathematical model for predicting the local and total deposition of hygroscopic particles in the human airways. The predictive model should have application in aerosol therapy.